In cellular radio systems, which are generally referred to as mobile communication systems herein, the geographical area covered by the system is divided into smaller radio areas, i.e. radio cells, to make the utilization of the frequency band of the system more efficient. Mobile radio stations, i.e. mobile stations, may freely move from a cell to another within the system area. In order that mobile-terminating calls and signalling can be routed to the correct location in a cellular radio network, the cellular radio network maintains the location data of mobile stations in the subscriber databases of the cellular radio network.
Typically, a cellular radio network knows the location of mobile stations with an accuracy of a so-called location area, which consists of one or more cells, (By this, it is meant that the cellular radio network knows which location area each mobile station is located in, but not necessarily in which cell within a location area each mobile station is located.) i.e. a group of cells. The location data of a mobile station in subscriber databases is updated only if the mobile station moves from a location area into another. This type of location updating based on a location area is a compromise between location updating carried out in each cell and PLMN-based (Public Land Mobile Network) location updating. The disadvantage of PLMN-based location updating is that in a case of a mobile-terminating call, the paging message is transmitted in all cells within the PLMN. Furthermore, all paging messages are repeated, for instance three times, to increase the probability of reception. This manner of proceeding consumes the frequency band. In a case where location updating takes place in connection with every cell crossover, there is a significant increase in the number of location updating messages. This consumes the capacity of the radio path, and the need for data processing in mobile services switching centers and base station controllers also increases.
The location updating and location management based on location areas operate in a satisfactory manner in conventional networks.
Finnish Patent Applications 933,894 and 940,314, which are unpublished on Apr. 8, 1994, disclose new packet data transfer modes between a mobile station and a special data service center. The packet service center produces an interworking function between the cellular radio network and a separate data network. Data packets are transmitted between a mobile station capable of data transmission and the packet service unit by using a so-called virtual connection. In this case, 1) a circuit-switched connection through the cellular network is only established for the period of time required for transmitting a single packet or 2) packets are transferred through the cellular radio network on the basis of the address on a data packet according to the node-to-node scheme entirely without a circuit-switched connection by using the network elements of the cellular network as nodes.
In the first case, described in Finnish Patent Application 933,894, the data service center informs a mobile station, via a common downlink paging channel, of an incoming data packet transmission, as a result of which the mobile station initiates the establishment of a circuit-switched connection in the network by using call set-up data associated with the virtual connection. When the packet transmission has been completed, the circuit-switched connection is immediately released and only the virtual connection, i.e. the switching data of the connection, is retained. Informing of incoming data transmissions takes place in cells via common paging channels by using paging messages. The number of paging messages relating to packet transmission in cells thus radically increases with the number of subscribers using the packet service and the amount of packet transmission. If the location management of a cellular network is based on location areas, a mobile station is informed of an incoming data transmission by transmitting a paging message in each cell of the location area. As a result of this, the consumption of the frequency band is greatly increased. If, however, location information is maintained in the cellular network with an accuracy of one cell, the transmission of multiple paging messages is avoided but on the other hand, the amount of location updating in the entire cellular network increases.
In datagram-based connectionless packet transmission, disclosed in Finnish Patent Application 940,314, there is no circuit-switched path between a mobile station and the packet service center during data transmission. On the radio path, data packets are primarily transmitted by using a dedicated media access control, derived from Aloha-type or other expedited call set-up signalling. Thus, it is also necessary in this other method to transmit paging or packet messages to a mobile station on paging channels in a case of an incoming packet transmission, whereby a similar conflict between the optimization of the number of paging messages and the amount of location updating arises.